Clinical Dentistry and Basic Sciences

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NEW YORK (Reuters Health) Oct 22 - Plasma myeloperoxidase levels are elevated and glutathione peroxidase 1 activity is reduced in patients with chest pain who are at increased risk of cardiac events, according to two reports in October 23rd issue of The New England Journal of Medicine.

Myeloperoxidase, a product of activated leukocytes, is elevated in the presence of unstable atherosclerotic plaque, Dr. Stanley L. Hazen and colleagues at the Cleveland Clinic Foundation explain.

To evaluate the use of myeloperoxidase as a marker of plaque vulnerability, Dr. Hazen's group recruited 604 patients presenting to the emergency department within 24 hours after the onset of chest pain of suspected cardiac origin.

Median myeloperoxidase level was significantly higher among patients who had an MI within 16 hours after presentation than in those who did not (320 pM versus 178 pM, respectively, p < 0.001). Increased baseline levels were associated with patient mortality, MI or reinfarction, the need for revascularization within 30 days or within 6 months (p < 0.001 for all comparisons).

Even among patients with normal troponin T levels throughout the 16 hours after presentation, myeloperoxidase levels were significantly higher among patients who had major adverse cardiac events within the next 6 months. C-reactive protein levels, on the other hand, were not predictive of adverse cardiac events in this subset of patients.

Multivariate analysis revealed that myeloperoxidase level is an independent predictor of increased risk of a cardiac event. Combined testing of myeloperoxidase and troponin T predicted 84.5% of major cardiac events, compared with 58.0% for troponin T alone.

"The two proteins track different process," co-author Dr. Eric J. Topol told Reuters Health. "Troponin T tracks cell death, whereas myeloperoxidase indicates artery inflammation," making them both valuable markers for heart disease.

Dr. Topol predicts that an inexpensive commercial test for myeloperoxidase will be available soon, which will probably incorporate assays for multiple markers of inflammation and coronary risk.

In the second report, Dr. Stefan Blankenberg, at Johannes Gutenberg University Mainz, Germany, and colleagues report the findings of a prospective study of 636 patients with angiographically documented coronary artery disease.

During a median of 4.7 years' follow-up, 83 subjects had an MI or died of heart disease. Erythrocyte intracellular glutathione peroxidase 1 was inversely associated with future cardiovascular events.

In an accompanying commentary, Dr. Teri Manolio, from the National Heart, Lung, and Blood Institute in Bethesda, Maryland, points out that both enzymes possess two characteristics of an ideal risk marker: They provide independent information about a patient's risk and they account for a large proportion of the risk associated with heart disease.